Methods for producing sucralose intermediates and sucralose from a feed stream comprising a sucrose-6-acylate in a reaction vehicle are known. For example, EP 0409549 discloses a process for the chlorination of a sucrose-6-acylate in a tertiary amide reaction vehicle to produce a sucralose-6-acylate, such as sucralose-6-acetate. A large excess of an acid chloride, such as phosgene, is used as the chlorination agent in this process. Following the chlorination reaction, the excess chlorinating agent is quenched using a suitable base, thereby forming the chloride salt of the base. The resulting product stream thus comprises a sucralose-6-acylate, the tertiary amide reaction vehicle, water, and salts.
A known method for obtaining sucralose from a product stream comprising a sucralose-6-acylate, a tertiary amide reaction vehicle, water, and salts, without isolation of the sucralose-6-acylate intermediate, is disclosed in EP 0708110. The process comprises deacylation of the sucralose-6-acylate before or after removal of the tertiary amide reaction vehicle, and then isolation of the sucralose. Other methods of extraction of sucralose are known, for example, in U.S. Pat. No. 8,212,022.
Methods for preparing sucrose-6-acylate starting materials for chlorination to sucralose-6-acylate are known, for example, in U.S. Pat. Nos. 4,950,746; 4,889,928; 5,023,329; 5,089,608; 5,034,551; 5,470,969; 5,440,026; 6,939,962; and US 2007/0227897.
Other methods of chlorinating sucrose-6-acylate to give sucralose-6-acylate are known, for example, in U.S. Pat. No. 4,380,476; US 2006/0205936; U.S. Pat. No. 7,932,380; and US 2007/0100139.
It is often desirable to recover the reaction solvent after completion of a reaction to minimise waste, or to reuse the solvent. Particularly in sucralose synthesis, it is desirable to recover the tertiary amide from the reaction mixture after chlorination of a sucrose-6-acylate to a sucralose-6-acylate for reuse. U.S. Pat. No. 5,530,106 discloses a method of removing tertiary amide (which is usually N,N-dimethylformamide (“DMF”)) from a product mixture after quench by steam stripping.
U.S. Pat. No. 8,530,643 discloses a method of removing DMF from the reaction mixture in the chlorination of a sucrose-6-acylate to a sucralose-6-acylate, before quench of the reaction, by distillation, to afford DMF.
These methods of removing DMF require large amounts of energy to obtain DMF suitable for reuse. Accordingly there is a need for new methods of removing DMF from reaction mixtures.